Your Digest for Sunday, Jan 07, 2024 11:59 PM

Broadly, lymphoma is distinguished from leukaemia in its clinical presentation, where lymphoma predominately involves lymph nodes, and leukaemia the blood and bone marrow, and by the fact that lymphomas arise from cells that reside in the lymphatic system rather than in the bone marrow. However, in the context of the cell of origin this is perhaps a rather nebulous distinction, and there is evidence that chronic lymphocytic leukaemia (CLL) may emerge in differentiated/mature lymphocytes in the periphery
[!INFO] The correct identification of AML vs ALL is veryimportant as a determines treatment.

• Aggressive cancers
• Child with lymphocytosis must be evaluated. Hepatosplenomegaly, complaining of bone pain / limp are red flag signs!
• investigations focus on identifying haematologic malignancy and then identifying the type of malignancy (myeloid or lymphoid, subtypes of lymhpoid etc)

• Blasts can be of B cell lineage (commonest - 85%), T cell (15%) and NK cell (<1%). These can be distinguished by cell surface antigens.
  • T cell leukemias are commoner in 15-20 year olds and in males.
  • (Mnemonic: T for twenty)

Note : T cells are the commonest type of lymphocytes in healthy states, followed by B and NK cells.

• Can present as leukemi (blasts in blood with bone marrow involvement) or lymphoblastic lymphoma (mediastinal mass)

• Symptoms are non specific, similar to self limited diseases
• Fever (common), pallor, bleeding (+/-petechial rash), bone pain (can present as limp!, #hepatosplenomegaly, lymphadenopathy - HSM is the commonest clinical finding
• CNV involvement: headache, vomiting, nerve palsies from meningeal spread.
• WBC can be low, normal or high.
  • When gross malignant lymphocytosis develops, anaemia, thrombocytopaenia and neutropenia have usually developed.
• Peripheral blood can sometimes have no blasts but bone marrow will show blasts.

• B-type ALL (i.e of B lymphocytes) have the philadelphia chromosome. (9;22 translocation)

• more than 20% lymphoblasts
  

1. outside the usual age range (i.e worse prognosis if pt is infant or adolescent) because tumours with good prognosis karyotypes (t[12:21] and hyperploidy) are commoner in this age group.
2. Male gender
3. Philadelphia chromosome positive
4. Slow response to induction therapy (i.e more than 28 days)- (? children usually respond fast to induction therapy?)
5. Having Trisomy 21.

• Above is an image of the atypical lymphocytes in infectious mononucleosis. They represent activated T lymphocytes.
• Basophilic skirting occurs where lymphocyte cytoplasms abuts erythrocytes. Source

• #lymphadenopathy: Symmetrical, tender, posterior chain predominant
• Blood - lymphocytosis with atypical lymphocytes (mononuclear cells) - hence the name infectious mononucleosis.

• Chronic active EBV infection - Persistent IM like syndrome with continued viraemia. It's a life threatening lymphoproliferative disorder.
  EBV should be differentiated from Acute lymphoblastic leukemia which can occur in the same age group and have similar initial presentation.

[!INFO] The only 5 causes of hypoxaemia! (search: hypoxia)
[!INFO] The fundamental difference between O2 and CO2 exchange
With respect to alveolar gas:

• O2 is supplied by ventilation and removed by blood flow.
• CO2 is supplied by blood flow and removed by ventilation.
• Hypoventilation, thus, results in both hypoxaemia and hypercapnia
  One important aspect of O2 treatment in hypoxia due to hypoventilation is that hypoventilation, while breathing air, will result in severe hypoxaemia before _P_aCO2 increases to dangerously high levels. In contrast, providing supplemental O2 can result in _P_AO2 and _P_aO2 being maintained above 90 mmHg (12 kPa) even with hypoventilation causing severe hypercapnia. A clinically important corollary is that a normal pulse oximetry reading in a patient breathing air is a good indication of adequate ventilation (normal _P_aCO2). However, when a patient is on supplemental O2, a normal O2 saturation cannot be used to judge the adequacy of ventilation.